To clarify, when I mention songs that exclusively use the pentatonic scale, I am referring to the vocal melody. It would be very difficult to avoid ^4 and ^7 (or ^2 and ^6 in minor) when using diatonic triads as the underlying chords. I and vi would be the only viable options...

However, when used as chord tones in diatonic triads, tendency tones become significantly more stable and impose much less tonal gravity than they do as featured melodic notes.

But let me address specific chords.

In the case of ii and IV (or iv and VI in minor), since the melody is always perceived as being 'on top', a concurrent sounding of ^4 and ^3 (or ^6 and ^5 in minor) would not yield a harsh sounding minor 2nd, but a perceived major 7th. In the context of modern pop, a major 7th is not dissonant in the classical sense, but sounds like a relatively stable tonal coloring of the chord.

In the case of iii and V (or v and VII in minor), the presence of ^7 (or ^2) poses a bit more of a 'threat' for harsh clashes, but this is usually neutralized in one or more of the following ways:

Omitting the tendency tone from the chord (e.g., playing only ^5 and ^2 in place of a full V triad).

Displacing the tendency tone and playing a sus2 or sus4 chord.

Burying the tendency tone in the mix so it doesn't compete with the melody.

Including the tendency tone in a lush sonority that's perceived as being in a separate timbral space than the vocal melody.

​CONCLUSION

Pentatonic scales are extremely popular these days with pop songwriters because they allow for musical freedoms and interesting sonorities that would be difficult to achieve otherwise without venturing too far away from the pop sound.

They also lend themselves well to the collaborative nature of pop songwriting and production, making it easier to combine ideas and elements coming from different creative minds.

This does not mean that as a pop creator you should always stick to pentatonic scales - many hit pop songs use 'regular' major and minor scales, and some even use chromatic notes - but they can serve as an important tool in your creative arsenal.

​They certainly are for most hitmakers these days.

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